Thermoplastic seam



Dec. 4, 1962 H. G. CHINN THERMOPLASTIC SEAM Original Filed July 17, 1958INVENTOR HYMAN G. CHINN A 7'7'ORNE Y United States Patent Ofitice3,067,079 Patented Dec. 4, 1962 THERMOPLASTIC SEAM Hyman G. Chinn,Somerviile, N.J., assignor to Union Carbide Corporation, a corporationof New York Original application July 17, 1958, Ser. No. 749,274, nowPatent No. 3,018,212, dated Jan. 23, 1962. Divided and this applicationApr. 24, 1961, Ser. No. 104,927

5 Claims. (Cl. 154-43) This invention relates to thermoplastic edgedwebs and thermoplastic lined containers and a method for theirmanufacture.

This is a divisional application of my copending application Serial No.749,274, filed July 17, 1958, now US. Patent 3,018,212, issued January23, 1962.

Continuous thermoplastic coatings over both the surface and the edges ofsheet material have heretofore been generally unsatisfactory anddifiicult to obtain. In certain instances, as when the sheet materialhas been fabricated into a container, continuous thermoplastic coatingshave been impossible to obtain. Coating the fiat expanse of sheetmaterial faces is easily accomplished, but the edges of the sheetmaterial web cannot be successfully coated with thermoplastic by any ofthe presently known coating techniques.

The presence of a discontinuity in a coating such as is created by anuncoated and exposed sheet material edge almost completely nullifies theadvantages realized from coating the sheet material faces. Uncoatedsheet ma terial edges are a point, in an otherwise completely coatedcontainer, at which leakage can develop, if the packaged contents areliquid or even semi-liquid. In addition, contamination of the contentsby the elution of chemicals from the sheet material is a distinctpossibility. Thus the presence of even one uncoated edge interrupts theinert, chemically resistant, moisture and vapor impermeable barrierwhich resin coatings, when continuous, provide.

Inaccessibility of the edges, particularly after the sheet material hasbeen fabricated into a container, and coincidence of a sheet materialedge with a container edge preclude use ,of spray coating techniqueswhich are awkward, time consuming, and unreliable in these applications.Further, with thermoplastic resins, such as polyethylene, a problem ofadhesion to nonmetallic substrates arises, rendering spray-coatingtechniques even less desirable. In other applications, such as coatingof sharpedged webs with plastic to prevent their cutting, a convenient,widely adaptable method is not known. Dip coating techniques such as areused with wax coatings are not practicable with thermoplastics.

There are two general types of bonds employed to join or seal webs ofsheet material, a butt-joint or edge-to-edge bond, and a lap joint oredge margin-over-edge margin bond wherein the portion of sheet materialimmediately adjacent to the edge, or edge margin, is lapped over thecorresponding portion of the sheet material web. In the fabrication of apaper bag, for example, a web of sheet material is folded lengthwise andthe opposite edge margins are brought into contact with one another andbonded with a suitable adhesive. Thus there is a seam running the entirelength of the bag. If the bag is fabricated from sheet material coatedon the inner side, a continuous thermoplastic lining would be obtainedif a suitable bond were made between the edges. Generally a lap joint isemployed because it affords greater strength than butt joint bonds, andin many applications the extra bulk at the seam which invariablyaccompanies lap joints is not harmful. Whether bulky or not, the lapjoint exposes an edge of the Web inside the container which, ifuncoated, breaks the continuity of the thermoplastic lining and defeatsthe purpose of the coating. Bags with discontinuous linings are prone tounsightly staining and physical weakening due to seepage of thecontents. Because a butt joint generally lacks the necessary strengthfor most bag making and similar applications, it is not so widely used,although with such a joint adjacent, uncoated edges are co-extensive andare thus not exposed to the container contents and a bond of less bulkis obtained.

A bag with a long seam is only one of the many types of containers inwhich the problem of exposed uncoated edges arises. Others are spiralwound containers and convolute containers which offer greater rigidityand strength but are subject to the same limitations as bags withregards to liquid and semi-liquid goods. Also, in these containers, thebulk of a lap joint can become a serious drawback.

It is an object, therefore, of my invention to provide a method forforming a bond between webs of sheet material which possesses theadvantages but not the drawbacks of both the butt joint and the lapjoint.

It is another object of my invention to provide a joint between webs ofsheet material which is. moisture impermeable, non-bulky, and strong.

A very particular object of my invention is to provide containers havinga continuous plastic lining throughout.

These and other objects are accomplished in accordance with my inventionby extruding a bead of a thermoplastic onto the edge margin of a web ofsheet. material and flattening the extruded bead, as by a pair of pinchrolls,

so that a portion of the flattened bead adheres to the web.

edge margin of the sheet material and the remainder of the flattenedbead extends outwardly from the web edge,

margin as a skirt. Thereafter the sheet material can be fabricated intoa container by placing a skirted sheet material edge adjacent to asecond sheet material edge in such manner that the skirt of said skirtedsheet material edge overlaps the edge margin of said second sheet ma-.terial edge and placing adhesive therebetween and simultaneouslypressing said skirt and said edge margin against said adhesive to form ajoint therebetween.

The method of my invention utilizes one and preferably two extruders.The first extruder places a head of resin upon a travelling web of sheetmaterial near the edge. The bead after flattening adheres firmly to thesheet material and is sufliciently solidified to extend outwardlywithout outside support as a skirt. The second extruder places a bead ofhot resin between said skirt and a second web edge margin and said skirtand edge margin are then pressed against the hot bead and become firmlybonded together thereby. Additionally, in those instances in which thetwo web edges are aligned in substantially abutting relation, some ofthe resin from the second extruder may be squeezed between said edgesand form a bond therebetween as well. The bond, when formed, possessesthe valuable attributes of both an overlap seal and a butt joint sealand also avoids the disadvantages of both. The bond possesses greatstrength, is uniform, does not leak, does not expose an uncoatedsurface, is easily applied, is not bulky, and is universally adaptable.This combination of qualities has not been attained before. The jointproduced by the method of my invention is ideal in containers which areto package liquid, semi-liquid, and/or chemically active goods.

The method is extremely versatile in that the extruded head can be anythermoplastic composition and can be applied to virtually any web ofsheet material, regardless of thickness, whether single or multi-ply,e.g., paper, metal foil, coated paper, and laminates. The width andthickness of both the portion of the flattened bead adhering to the weband the portion protruding outwardly from the web, i.e., the skirt, canbe exactly controlled during the process.

Additional advantages will become apparent from a consideration of thedetailed description below of one embodiment of the invention which isdescribed in conjunction with the attached drawings in which:

FIGURE 1 is a diagrammatic isometric view of the apparatus according toand for carrying out the method of the preferred embodiment of thepresent invention,

' FIGURE 2 is a section taken along the line 22 of FIGURE 1,

FIGURE 3 is a pictorial view of the preferred embodiment of a product ofthe method of my invention, and

FIGURE 4 is a section taken along the line 4-4 of FIGURE 3. a

The method of my invention as particularly adapted to the formation ofspiral wound containers is shown in FIGURE 1. From a consideration ofthe figure, it will be seen that sheet material is withdrawn from asupply roll 12 at a constant rate along a predetermined path. Anextruder, not shown, with nozzle 14 is positioned above the travellingweb of sheet material 10 so as to be approximately A; inch from the edgeof the sheet material 10. A bead of molten resin 16 is forced from thenozzle 14 onto the sheet material 10 which advances with the resin bead16 through the nip of a pair of pinch rolls 18. The pinch rolls 18 serveto flatten the resin bead 16, causing it to adhere to the sheet material10 and to extend outwardly from the sheet material 10 in aselfsupporting manner as a skirt 20. The relation of the skirt 20 andthe sheet material 10 is best shown in FIG- URE 2.

In order to form a spiral wound container such as shown in FIGURE 3, thesheet material 10 with skirt 20 is wound around fixed mandrel 22. Aparaffin-waxed paper slip sheet 24 is wound simultaneously with andslightly ahead of the sheet material 10 to ensure easy removal of thetube formed. A second extruder or sealer with nozzle 26 places adhesivebead 28' on the skirt 20 of sheet material 10. Winding of sheet material10 about the mandrel 22 is accomplished in a manner which places edgemargin 34 adjacent to edge margin 36. In the specific embodiment shown,the edges of the respective edge margins 34 and 36 are in abuttingrelation, however, it is within the scope of my invention for edgemargins 34 and 36 to be in overlapping relation. In FIGURE 1, as thesheet material 10 is wound, skirt 20 is positioned in contact with slipsheet 24 against mandrel 22. Successive turns of sheet material 10 placeedge margin 36 of sheet material 10 in overlapping relation with skirt20. The nozzle 26 places a bead of adhesive between skirt 20 and thenext turn of sheet material 10. The pressure induced by the windingaction forces edge margin 36 against skirt 26 to form a bond such asshown in FIGURE 4. The bond hardens and the spiral wound container iscut as withdrawn from the mandrel and appears in FIGURE 3.

Various modifications such as formation of two skirts simultaneously andalternate embodiments of our invention such as bag and convolute woundcontainer manufacture are obvious to those skilled in the art.

The scope of my invention, therefore, is not limited except as definedin the appended claims.

What is claimed is:

1. A sheet material container having a moisture proof seam comprisingcontoured sheet material and wherein adjacent edges of said sheetmaterial define a seam and extending from the edge margin of the firstsheet to the edge margin of the second sheet across said seam ahardened, self-supporting skirt of thermoplastic which is heat andpressure bonded to the edge margin of said first sheet and adhesivebonded to the edge margin of said second sheet.

2. The sheet material container claimed in claim 1, wherein the seam isa lap joint seam.

3. The sheet material container claimed in claim 1 wherein the seam is abutt joint seam;

4. A tubular sheet material container having a moisture proof seamcomprising spiral wound sheet material and wherein adjacent edges ofsaid Wound sheet material define a seam and extending from the edgemargin of one turn of the sheet material to the edge margin of the nextturn of the sheet material across said seam a hardened, self-supportingskirt of thermoplastic which is heat and pressure bonded to one edgemargin and adhesive bonded to the other edge margin.

5. The tubular sheet material container claimed in claim 4 wherein theentire interior surface of the container is plastic coated.

References Cited in the file of this patent UNITED STATES PATENTS2,415,906 Paige Feb. 18, 1947 2,677,633 Gross May 4, 1954 2,943,540McBain July 5, 1960

1. A SHEET MATERIAL CONTAINER HAVING A MOISTURE PROOF SEAM COMPRISINGCONTOURED SHEET MATERIAL AND WHEREIN ADJACENT EDGES OF SAID SHEETMATERIAL DEFINE A SEAM AND EXTENDING FROM THE EDGE MARGIN OF THE FIRSTSHEET TO THE EDGE MARGIN OF THE SECOND SHEET ACROSS SAID SEAM AHARDENED, SELF-SUPPORTING SKIRT OF THERMOPLASTRIC WHICH IS HEAT ANDPRESSURE BONDED TO THE EDGE MARGIN OF SAID FIRST SHEET AND ADHESIVEBONDED TO THE EDGE MARGIN OF SAID SECOND SHEET.